These rare cars aren't safe for the road but make great investments

Riding a motorized sofa down I-95 might seem like fun. But it's not safe. Or particularly legal.

For this, we can thank the National Highway Traffic Safety Administration.

(Seriously. We should thank them for this.)

The NHTSA, officially formed by the United States Department of Transportation in 1970, is the governing body when it comes to minimum safety performance requirements. These are the guidelines any car must follow in order to ride on federal roads.

The first such guideline for the Federal Motor Vehicle Safety Standards and Regulations was established in 1967, and it detailed requirements of "seat belt assemblies."

Since then, rules and regulations have changed and adapted to advancements in automotive technology, all while still maintaining the sensibilities that prevent you from legally driving a La-Z-Boy to Hilton Head for Memorial Day Weekend.

Some classic cars don't meet these standards. But just because they're not street legal doesn't mean they're not good investments.

In the above video from CNBC's "Jay Leno's Garage," Leno and automotive valuation expert Donald Osborne discuss three different unique cars that wouldn't make the grade. Watch to see how these vehicles appreciated over time.